A filter device for removing fiber fragments from air is described in German Patent 14 04 894. Each portion of the collecting device is formed by two vertical filters disposed so as to form a V. Each V portion is associated with a corresponding V-shaped blow-pipe system which is moved up and down for pneumatically cleaning the associated V-portion of the collecting device.
Each V-portion of the collecting device can be closed by a lamellar shutter at the inlet to the interior of the V-portion to prevent exhaust air from flowing in for purification.
In order to clean a selected V-portion, the shutter is closed and the blow-pipe system associated with the V-portion can then be moved up and down so as to blow off the impurities which have accumulated on the V-portion, so that they fall onto the base of the V-portion and can e.g. be pneumatically sucked therefrom. This filter system is complicated in construction, uses a relatively large amount of energy for pneumatic cleaning, and is completely unusable for filtering air during the cleaning of a V-portion.